import math

x1,y1,x2,y2 = map(float,input().split(" "))
print("{:.5f}".format(math.sqrt((x2-x1)**2 + (y2-y1)**2)))

 import math math x1,y1,x2,y2 = map(float,input().split(" ")) x1 map(float,input().split(" ")) map float input().split(" ") ().split () input split " " y1 x2 y2 print("{:.5f}".format(math.sqrt((x2-x1)**2 + (y2-y1)**2))) print "{:.5f}".format(math.sqrt((x2-x1)**2 + (y2-y1)**2)) "{:.5f}".format "{:.5f}" format math.sqrt((x2-x1)**2 + (y2-y1)**2) math.sqrt math sqrt (x2-x1)**2 + (y2-y1)**2 (x2-x1)**2 x2-x1 x2 x1 2 (y2-y1)**2 y2-y1 y2 y1 2 x1,y1,x2,y2 = map(float,input().split(" ")) map(float,input().split(" ")) x1 y1,x2,y2 = map(float,input().split(" ")) map(float,input().split(" ")) y1 y2 = map(float,input().split(" ")) map(float,input().split(" ")) y2 x2,y2 = map(float,input().split(" ")) map(float,input().split(" ")) x2
import math

x1,y1,x2,y2 = map(float,input().split(" "))
print("{:.5f}".format(math.sqrt((x2-x1)**2 + (y2-y1)**2)))


